1. Technical Field
The present disclosure relates to a method of fabricating a semiconductor device, and more particularly, to a method of fabricating a self-aligned contact (SAC) pad using a chemical mechanical polishing (CMP) process.
2. Description of the Related Art
As semiconductor devices have become highly integrated and design rules have become stricter, obtaining a sufficient process margin is regarded as a significant factor when forming contact pads to connect transistors to lines such as bit lines or transistors to capacitors. Accordingly, forming a self-aligned contact (SAC) pad self-aligned with a line such as a gate line becomes significant.
For example in forming a conventional SAC pad, a capping layer of a line and a spacer serve as an etch stop layer when forming an opening hole for a contact pad to pass through an insulation layer, such that the opening hole can be self-aligned with the line. Moreover, as a photoresist mask having an opening region larger than that of the opening hole can be used as an etching mask, a more sufficient process margin of a photolithography process can be obtained.
However, as the design rules of semiconductor devices have been significantly reduced, there is a demand for an improved method for obtaining a sufficient process margin for a photolithography process when forming a photoresist mask.
Moreover, when forming a conductive layer that fills the opening hole and forming each SAC pad, the resulting structure having the SAC pad has a more planarized surface by using a chemical mechanical polishing (CMP) process as a SAC pad node separation method. Furthermore, a subsequent process can be performed on the more planarized surface such that a sufficient process margin for the subsequent photolithography process can be obtained.
Also, during a conventional SAC pad process, the separating of the SAC pad using a CMP process is used to overcome the limitation of the design rules. Additionally, detecting an end point of a CMP process becomes significant for accurately controlling the CMP process.
However, a difficulty with conventional SAC pad process, may be that when selectively etching an opening hole during the SAC pad process, a capping layer for a line and/or a spacer for an etch stop layer can be unnecessarily removed. Therefore, the detection of the end point of the CMP process becomes more difficult.
For example, the thickness of a capping layer in a region that is covered by a photoresist mask used for an etching mask when etching the opening hole can be different from the thickness of a remaining capping layer in a region that is uncovered by a photoresist mask. The covered capping layer is undesirably etched during the CMP process. Consequently, as the thickness of the capping layer below the conductive layer for the SAC node varies according to a region, the height of the capping layer is varied when using the capping layer as an end point of the CMP process. Therefore, with the above conventional SAC pad process, the accurate detection of the end point becomes more difficult, and thus it may also be difficult to achieve reliable node separation.
Consequently, as a result of the above-mentioned difficulty of a conventional SAC pad process in detecting a CMP end point, after a CMP process, a local height difference can occur between the region where the SAC pad is formed and the region where the SAC pad is not formed. The height difference can be a factor that limits the process margin of the following photography process.
Moreover, when the CMP end point is not detected accurately, a relatively large number of methods of performing a CMP process may be required to obtain reliable node separation. These additional CMP processes can damage the capping layer and the spacer.
The above-mentioned damage to the capping layer and/or spacer may cause the thickness of the capping layer and/or the spacer that protect lines to decrease (e.g. a shoulder margin deficiency phenomena occurs), thereby resulting in an electrical short occurring between a first line (e.g., a gate line) that should be protected by the capping layer and the spacer, and a second line (e.g., a bit line) that is electrically connected to the SAC pad.
Accordingly, to prevent electrical shorts and a local height difference, a method of stably and accurately detecting the CMP end point should be utilized during node separation in the SAC pad process using a CMP process.
Thus, there is a need for a method of fabricating a self-aligned contact (SAC) pad of a semiconductor device, which obtains an improved process margin for a photolithography process that is used to form an opening hole for a SAC pad, and which may stably detect a chemical mechanical polishing (CMP) end point.